I have a Baxi 130 HE. Last night the pressure was low so I topped it up to the middle of the green. The system seems to be grumbling to itself with a ticking noise. When the thermostat turns the pump and the unit fires up the grumbling sound turns to a moan which occurs every 40secs or so and the radiators only seem to get tepid. Can anybody give me a clue as to what is wrong.
